This invention relates to sealing means between adjacent relatively rotatable members. More particularly, this invention relates to durable sealing means for rotating shafts such as crank shafts of diesel engines whereby fluid leakage between the rotating shaft and adjacent fluid-containing means may effectively be prevented.
It is well known in the art to provide rotating-shaft seals for preventing leakage of fluid, most usually lubricant, between the shaft and an associated fluid-containing chamber, as well as for preventing the entry of dust or other foreign matter into this chamber. Although many of these prior art seals are relatively satisfactory with respect either to durability or to sealing characteristics, typical shaft seals in present use do not possess both these qualities to a satisfactory degree for many applications.
For example, problems are frequently encountered in providing satisfactory front and rear shaft seals for the crankshaft of diesel engines. It is important that these seals prevent leakage of lubricating oil from the engine compartment, out of which the crankshaft extends, as well as prevent entry of foreign matter into the engine compartment. However, both the large diameter of the crankshaft and the loads imposed thereupon create operating conditions under which conventional sealing means are frequently not effective in terms of preventing leakage of lubricant, or are not satisfactory in terms of durability.
The large diameter of the crankshaft, required for adequate strength, results in a high peripheral speed between the seals and the crankshaft which tends to shorten the life of the seals, particularly the rear seal between the crankshaft and flywheel housing. Owing to the time required to replace a failed seal because of the necessity of removing various parts, such as the flywheel, to gain access to these seals, it is highly desirable that these shaft seals be extremely durable, preferably having a wear life of at least 20,000 hours of heavy duty engine operation.
Additionally, as a result of the loads imposed on the crankshaft during operation, the crankshaft goes through exursions as great as about 0.020 radially and at least equal amount axially; if adequate sealing is to be obtained, the seal must follow the crankshaft through all of these motions. Further, the crankshaft seals are frequently subjected to differential pressure caused for example by internal crankcase pressures or by a head of oil being built up within the engine. It is highly desirable that sealing means be provided which substantially eliminate lubricant leakage under all these conditions, whether or not the engine is operating.
Typical shaft seals in present use include piston ring-type seals, such as described in U.S. Pat. No. 3,211,467 and lip type seals. In the piston ring-type seals, the ring is seated very closely in a groove, whereby leakage of lubricant is reduced depending on the closeness of the fit of the ring in the groove. Since relative motion must be permitted between ring and groove, the fit is never perfect, and some leakage inevitably occurs, particularly when the engine is not operating. Such leakage is generally undesirable, and in some applications, such as generators, not permissible for satisfactory engine operation. In the lip-type seal, an elastomeric member is fitted against the crankshaft to provide a generally effective seal against lubricant leakage. However, this type of seal has minimal durability, and the action of the crankshaft rubbing against the elastomer frequently results in early seal failure, thereby necessitating time-consuming seal changes. Also, this type of seal is very sensitive to pressure differentials between adjoining sealed chambers, such as frequently occur, for example, between the crankcase and transmission compartment or atmosphere in piston engines because of blow-by pressure around the piston rings. The susceptibility of this type of seal to leakage under such pressure conditions renders it unsatisfactory for use with certain transmissions.